Multiphase converter with zero voltage switching
A multiphase DC-to-DC converter includes at least two phase circuits each having upper and lower power switches and a front-end inductor that is operative for forming a resonant tank circuit with the phase circuits to ensure zero voltage switching and minimizing power losses.
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This application is based upon prior filed copending provisional application Ser. No. 60/538,091 filed Jan. 21, 2004.
FIELD OF THE INVENTIONThe present invention relates to the field of electronic circuits, and more particularly, to DC-to-DC converters and switch mode power supplies for example, Buck converters.
BACKGROUND OF THE INVENTIONDC-to-DC converters typically are designed as switching-regulated power supplies also known as a switch-mode power supplies. Some DC-to-DC converters raise voltage from a lower input voltage (a step-up converter), and others lower voltage from a higher input voltage (a step-down converter). One type of step-down switch mode power supply that lowers the voltage is known as a Buck converter, a type of switch mode regulator/or switching power supply. These devices resemble a linear power supply in some respects, but in other ways they are much different. A switching power supply typically includes an energy-storage inductor, and sometimes a non-linear regulator network. This type of power supply can incorporate a regulation system in which a control element, for example, power MOSFET switches, are switched on and off rapidly. The on/off pulses can be controlled by an oscillator/error amplifier/pulse-width modulator network as a controller. Thus, in a more common variety of switching regulator, the transistor switch, for example, the MOSFET, is a control element.
During an ON cycle, energy can be pumped into an inductor and stored in magnetic fields. When the control element is turned OFF, the energy is stored and the inductor is directed by a diode into a filter and load. Various sampling circuits can sample the output voltage and feed a sample to an input of an error amplifier as part of a controller. The sample voltage can be compared with a reference voltage and an error amplifier can increase its output control voltage, which is sent to a pulse-width modulator. The pulse-width modulator produces a modified ON/OFF signal, for example, sometimes a square wave whose time is determined by the input error voltage.
More specific examples of DC-to-DC converters as switch mode power supplies are disclosed in commonly assigned, published U.S. patent application nos. 2003/0038614 and 2004/0070382, the disclosures which are hereby incorporated by reference in their entirety. As noted before, a Buck converter is a specific type of step-down, DC-to-DC converter.
To power various microprocessors, and more particularly the next generation microprocessors, requiring about one volt and up to 1,000 amps current, the number of phases in a multiphase Buck converter has been increasing, sometimes requiring as many as eight phases. The optimum number of phases can be determined by the output current, system efficiency, transient requirements, thermal management, cost of capacitors, MOSFET performance, size restriction and overall system costs. A controller for Buck converters is complicated and typically is designed as a multiphase PWM control integrated circuit with companion gate drivers, e.g., the HIP6301, HIP6601B, HIP6602B, HIP6603B, or HIP6604B and external MOSFET's, for example as manufactured by the assignee of the present invention, Intersil Americas Inc.
Multiphase power conversion is an improvement over earlier single phase converter configurations and is used to satisfy the increasing current demands of modern microprocessors. Multiphase converters distribute the power and load current, which results in smaller and lower cost transistors with fewer input and output capacitors. This occurs because of higher effective conversion frequency with higher frequency ripple current and phase interleaving. Each phase circuit typically includes a lower MOSFET and an upper MOSFET as power switches. The requirement for decreasing the size of the converter along with the requirement for higher power densities requires an increase in the switching frequency used in the power converter. The use of a high switching frequency, in these multiphase DC-to-DC converters, and especially Buck converters, however, leads to switching losses, stresses on the power component, and EMI generation.
SUMMARY OF THE INVENTIONThe present invention is advantageous and improves the efficiency of a switch mode power supply, DC-to-DC converter because it is operable for zero voltage switching and can be used for non-isolated high input/low voltage output voltage converters, such as a Buck converter. The present invention uses a resonant tank circuit for a multiphase topology. The Vout/Vin DC transfer function depends on N number of phases. With the present invention, it is possible to achieve higher than normal output ripple cancellation than with existing Buck topologies.
In the present invention, the duty cycle is no longer a function of only the time ON but it is a function of the time ON and the number of phases (N). The present invention detects the zero crossing, for example, using a PWM controller or other Buck controller. In the present invention, it is possible to create a zero voltage across the upper MOSFET before the MOSFET's are turned ON or OFF. A resonant tank is created that achieves zero voltage across the MOSFET's before they are turned ON or OFF as part of the improved topology. The front-end inductor creates a desired resonant tank circuit.
Typically the MOSFET has an inherent parasitic capacitance as part of a resonant tank. If the inherent parasitic capacitance is too small, it is possible to add a capacitor. A diode can also be added if the intrinsic diode capability of a MOSFET is insufficient.
In accordance with the present invention, the inductor at the front end does not allow the current to increase until a MOSFET is fully ON. There is no overlapping of current until the MOSFET turns ON. As to the inductor, its transition is smoother and the diode is slowly turning OFF instead of switching. Thus, it can be seen that there is zero current across the upper MOSFET and zero voltage across the lower MOSFET. The inductor resonates with any capacitors of the upper MOSFET's. Because of the resonant tank circuit, the time ON is fixed, but the time ON can vary according to what the controller signals. A total period for each phase is changing and time is variable, notably because the time ON is variable by the controller. The present invention is also operable because there is a time period when all lower MOSFET's are ON, and that time period is taken advantage of because of the resonance.
In accordance with the present invention, a multiphase DC-to-DC converter includes at least two phase circuits, each having upper and lower power switches and a front end inductor operative for forming a resonant tank circuit with the phase circuits to ensure zero voltage switching and minimizing power losses. The converter includes a controller operative with the phase circuit for detecting a zero volt crossing. The controller could be a PWM controller or other Buck controller. The resonant tank circuit is created to achieve zero voltage across the power switches, which typically are formed as field effect transistors. The converter could include a feedback signal processing circuit operative with each phase circuit and an output capacitor operative with the voltage output from the phase circuits. A capacitor can be operative with at least each upper power switch and lower power switch. A diode can also be operative with the upper power switch and lower power switch. These capacitors and diodes can be added if the intrinsic capacitance or diode function of the power switch is not enough to form the resonant tank circuit.
BRIEF DESCRIPTION OF THE DRAWINGSOther objects, features and advantages of the present invention will become apparent from the detailed description of the invention which follows, when considered in light of the accompanying drawings in which:
The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout, and prime notation is used to indicate similar elements in alternative embodiments.
The present invention improves the overall efficiency of the DC-to-DC converter system because zero voltage switching can be used for non-isolated high input voltage, and low output voltage power converters, for example, “Buck converters.”
The need for decreasing the size of the converter, along with the need for higher power densities, implies an increase of switching frequency used in the power converter. The use of high switching frequency, however, leads to switching losses, imparted stresses on the power components, and EMI generation. To overcome this disadvantage, soft switching zero voltage switching is used in the present invention.
In accordance with the present invention, to have zero volt switching, an inductor 60 is placed in front of the normal switching circuit at the front end of the circuit, as illustrated, and receives input voltage from the input voltage source 61. The control scheme is also changed to detect zero voltage, as will be explained in further detail below. The inductor 60 is resonating with the capacitors 54 of the upper MOSFET's in each of the phases.
With reference again to
The circuit was simulated as shown in the functional circuit representations shown in
Where θ is ton/toff, for example, as shown in
At to, as shown in
At t2, the inductor current reaching the output current (Mode 2), which is reflected in the functional drawing of
A state plane diagram is shown in
The present invention allows zero voltage switching. Referring again to
When the mode of operation is t<to=0, the mode of operation can be expressed as a circuit function in
The normalized value of V is
for I(t) is
This results in:
Mode 2 of operation, t1<t<t2 is shown by way of example to the circuit of
At a normalized solution:
Mode 3 of operation corresponds to t2<t<t3 as is shown in
ir(t2)=Ir2 VCr(t2)=Vm
The normalized solution is:
The state plane diagram for this type of function is shown in
Simplified equations for the circuit functions can be expressed as using:
The circuit functions with conservation of energy are expressed as:
Where D is:
Using the conservation of energy, it is possible to obtain D as a function of β and θ:
D=f(β, θ)
A graphical example of this conservation of energy is shown in the graph of
Generalized solutions for the duty, time ON and number of phases (n) are shown in the three-dimensional graph of
A spice model set-up circuit is shown in
A graph showing a state plane full load is shown in
Many modifications and other embodiments of the invention will come to the mind of one skilled in the art having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is understood that the invention is not to be limited to the specific embodiments disclosed, and that modifications and embodiments are intended to be included within the scope of the appended claims.
Claims
1. A multiphase DC-to-DC converter comprising:
- at least two phase circuits, each having upper and lower power switches; and
- a front-end inductor operative for forming a resonant tank circuit with said phase circuits to ensure zero voltage switching and minimizing power losses.
2. A multiphase DC-to-DC converter according to claim 1 and further comprising a controller operative with a phase circuit for detecting a zero volt crossing.
3. A multiphase DC-to-DC converter according to claim 2 wherein said controller comprises a PWM controller.
4. A multiphase DC-to-DC converter according to claim 1 wherein said resonant tank circuit is created to achieve zero voltage across said power switches.
5. A multiphase DC-to-DC converter according to claim 1 wherein said upper and lower power switches comprise field effect transistors.
6. A multiphase DC-to-DC converter according to claim 1 and further comprising a feedback signal processing circuit operative with each phase circuit.
7. A multiphase DC-to-DC converter according to claim 1 and further comprising an output capacitor operative with a voltage output from said phase circuits.
8. A multiphase DC-to-DC converter according to claim 1, and further comprising an output inductor operative within each phase circuit.
9. A multiphase DC-to-DC converter comprising:
- at least two phase circuits, each having upper and lower power switches and a capacitor operative with at least each upper power switch; and
- a front-end inductor operative for forming a resonant tank circuit with said upper power switches and capacitors to ensure zero voltage switching and minimizing power losses.
10. A multiphase DC-to-DC converter according to claim 9 wherein an upper capacitor is connected in parallel to a respective upper power switch.
11. A multiphase DC-to-DC converter according to claim 9 and further comprising a diode operative with each upper power switch to enhance zero voltage switching.
12. A multiphase DC-to-DC converter according to claim 9 and further comprising a diode operative with each lower power switch to enhance zero voltage switches.
13. A multiphase DC-to-DC converter according to claim 9 and further comprising a lower capacitor operative with each lower power switch.
14. A multiphase DC-to-DC converter according to claim 9 and further comprising a controller operative with a phase circuit for detecting a zero volt crossing.
15. A multiphase DC-to-DC converter according to claim 14 wherein said controller comprises a PWM controller.
16. A multiphase DC-to-DC converter according to claim 9 wherein said resonant tank circuit is created that achieves zero voltage across said power switches.
17. A multiphase DC-to-DC converter according to claim 9 wherein said upper and lower power switches comprise field effect transistors.
18. A multiphase DC-to-DC converter according to claim 9 and further comprising a feedback signal processing circuit operative with each phase circuit.
19. A multiphase DC-to-DC converter according to claim 9 and further comprising an output capacitor operative with a voltage output from said phase circuits.
20. A multiphase DC-to-DC converter according to claim 9, and further comprising an output inductor operative with phase circuits.
21. A method for regulating a multiphase DC-to-DC converter comprising:
- forming a resonant tank circuit with phase circuits using a front end inductor; and
- switching power switches in the phase circuits at zero volts to ensure zero voltage switching and minimizing power losses.
22. A method according to claim 21 wherein the method further comprises detecting a zero volt crossing.
23. A method according to claim 21 wherein the method further comprises forming a resonant tank circuit with capacitors operative with said power switches.
24. A method according to claim 21 wherein the method further comprises forming a resonant tank circuit with diodes operative with said power switches.
Type: Application
Filed: May 24, 2004
Publication Date: Jul 21, 2005
Patent Grant number: 7138789
Applicant: Intersil Americas Inc., State of Incorporation: Delaware (Milpitas, CA)
Inventors: Zaki Moussaoui (Palm Bay, FL), Thomas Victorin (Palm Bay, FL)
Application Number: 10/852,603